1. Field of the Invention
This invention relates to fence structures and more particularly to fences which are meant to restrain or prohibit the passage of human beings onto highways or over the side of bridges.
2. Description of Related Art
The fences placed along highways and over bridges to restrain human movement are subject to a variety of destructive forces. Most frequently, the fences are struck by moving vehicles. Unlike the typical guard rail fencing which is principally designed for impact, the open screening typically used in restraint fencing and the lighter weight of the upright posts usually results in structural failure of the fence under the force of even a modest impact. Often the fence components themselves become a further danger to nearby persons or vehicles as they hurl through the air after an impact.
A typical prior art screening fence consists of a fence panel section containing the restraint fabric which is attached to upright posts spaced at even intervals. Usually the upright posts are solid or hollow square bars or tubes onto which mounting plates have been attached either by welding or with bolts. The fence panel sections are attached to the mounting plates by bolts. When hit, this type of fence design usually fails at the mounting plate weld or attachment which is substantially weaker than the structural upright.
Another problem encountered with screening fence is the persistence of vandals in creating their own passageway through the fence. Usually the bolts fastening the fabric to the fence panel frame sections are removed by the vandals thereby permitting the fabric to be bent back. The replacement of the fabric and bolts can be a costly and time consuming maintenance task, especially since most screening fences are custom made to size rather than being assembled from stock components. This custom design also contributes to the frequency with which fences are given their final protective coating against the elements on site after they are erected.
Many alternative designs are known in the prior art for constructing highway screening and other types of fencing. No design is known which anticipates the combination of features of the present invention. For instance, U.S. Pat. No. 4,083,535 by Britt teaches a portable fence assembly in which the individual fence panels have wheels attached to the end members which fit into receiving channels in the upright support posts. U.S. Pat. No. 3,385,567 by Case and Belcher discloses a fence in which an upper frame member mounted in channels in the upright posts supports a web which rests directly on the support costs to suspend the panel arrangement. In U.S. Pat. No. 3,799,506 Schwartz teaches the use of fence panels mounted between upright slotted posts in an aluminum imitation of a woven wood fence. However, the end rails of the panel sections are slidably mounted within the top and bottom rails of each fence section so that they may be tensioned against the next panel in line mounted on the opposite side of the support cost. The fence sections are actually secured to each other with no tension being applied to the support posts.
In U.S. Pat. No. 4,193,584 Wieser discloses a livestock fence in which the concrete panels making up each fence section are held in vertical slots between concrete posts with the weight of each concrete panel resting on the ground. Restraining straps keep the concrete panels in place when jostled by the animals. U.S. Pat. No. 3,770,245 by Murdock teaches a fence assembly in which the fence panels are mounted on the support posts by a type of tongue and groove arrangement. In U.S. Pat. No. 4,306,631 Reusser teaches the use of I-beams for the vertical support posts. However, the interlocking vertical panels of his fence are secured to the opposite ends or flanges of the I-beam to form a staggered arrangement of panels. Finally, U.S. Pat. No. 4,071,223 by Demarest demonstrates a method of using vertical I-beams to support top and bottom horizontal rails which are mounted to the I-beams by angel brackets. Vertical strips are then fastened to the horizontal rails to fill in the fence.